L-tryptophan, which is an essential amino acid, has been widely used as a raw material for pharmaceutical products, such as feed additives, infusion solutions, etc., and has also been widely used as a health food ingredient, etc. L-tryptophan can be produced by a chemical synthesis method, an enzyme reaction method, a fermentation method, etc., but the direct fermentation method using a microorganism is mostly used at present.
A microorganism has an aromatic biosynthetic pathway, in which phosphoenol pyruvate (PEP), which is an intermediate in glycolysis, and erythrose-4-phosphate (E4P), which is a product of the pentose phosphate pathway, initiate polymerization by 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase (EC 2.5.1.54). In the pathway above, PEP and E4P are each conjugated to phosphate, and are substances containing high energy. Further, in the subsequent aromatic biosynthetic pathway, PEP is involved in the reaction when the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase (EC 2.5.1.19) reaction is carried out, and PRPP is used in the anthranilate phosphoribosyltransferase reaction. Accordingly, it is known that a large amount of high energy substances is required for tryptophan biosynthesis. According to previous studies, it was demonstrated by intracellular quantitative analysis that the highest level of energy is required for biosynthesis of tryptophan from among 20 amino acids (Proc. Natl. Acad. Sci. USA, (2002) V99, pp 3695-3700). Therefore, it can be considered that PEP and E4P play a significant role in strains producing tryptophan at high concentration in terms of continuous supply of precursors and efficient use of energy.
Accordingly, in order to stably supply E4P, the method of increasing the biosynthesis by enhancing the expression of tktA genes (NCBI gene ID: 12931960), which encode transketolase (EC 2.2.1.1), has been used most (Current Opinion in Biotechnology, (2009) V20, pp 651-658). In addition, numerous studies on reducing the use of ATP, which is a high energy substance, are underway in order to maintain intracellular energy level (FEMS Microbiol Lett, (2009) V297, pp 217-224). However, it is still necessary to develop a method for producing L-tryptophan in high efficiency.